Year	Percent
1960	2.83571
1961	2.82617
1962	2.79162
1963	2.81469
1964	2.85898
1965	2.91624
1966	2.99652
1967	3.01321
1968	2.94575
1969	2.71985
1970	2.41974
1971	2.11446
1972	1.87111
1973	1.67214
1974	1.54492
1975	1.4764
1976	1.4061
1977	1.35376
1978	1.43215
1979	1.66986
1980	1.99684
1981	2.33864
1982	2.63101
1983	2.81287
1984	2.86259
1985	2.81264
1986	2.77875
1987	2.76387
1988	2.66495
1989	2.45035
1990	2.20104
1991	1.88768
1992	1.65579
1993	1.68349
1994	2.03268
1995	2.58875
1996	3.19208
1997	3.64402
1998	3.84123
1999	3.7259
2000	3.40905
2001	3.0538
2002	2.79297
2003	2.60641
2004	2.55287
2005	2.57019
2006	2.60283
2007	2.60049
2008	2.56658
2009	2.50427
2010	2.41666
2011	2.33078
2012	2.25541
2013	2.19724
2014	2.15938
2015	2.13628
2016	2.11122
2017	2.08385